As the electrostatic chuck, there is conventionally known one which is provided with: a chuck plate made of a dielectric material; and a first electrode and a second electrode, both electrodes being disposed in the chuck plate such that a voltage is applied between the first and the second electrodes to thereby attract a to-be-processed substrate to the surface of the chuck plate (see, e.g., patent document 1). In case the to-be-processed substrate is an insulating substrate, the to-be-processed substrate gets attracted to the surface of the chuck plate due to a gradient force that is generated by applying a voltage between the first and the second electrodes. In case the to-be-processed substrate is a non-insulating substrate, the to-be-processed substrate gets attracted to the surface of the chuck plate due to Coulomb force that is generated by applying a voltage between the first and the second electrodes.
By the way, if a substrate having translucency such as glass substrate, sapphire substrate and the like is subjected to plasma etching processing or plasma CVD processing, light from the plasma is irradiated to the to-be-processed substrate, and this light is incident into the chuck plate through the to-be-processed substrate. Then, part of the dielectric material that forms the chuck plate becomes electrically conductive through photoelectric effect, resulting in lowering in the attraction (or suction) force.
However, there has conventionally been taken no measures against this kind of lowering in attraction force. The lowered attraction force has become a factor in the occurrence of a positional deviation of the to-be-processed substrate on the electrostatic chuck.